Many manufacturing processes involve the close coordination of a series of steps that are synchronized cyclically in automatic machinery. The power and motion required for the operation is usually introduced into the machine by means of sprockets or gears affixed to certain shafts by means of shaft keys, and in a like manner the energy and appropriate motions are carried throughout the machine by other shafts and other keyed sprockets (gears) to perform the specific steps required. Due to various material behaviors and eccentricities characteristic of machinery, the desired timing relationships between shafts is not always forthcoming. Means must be available to adjust these various shafting timing relationships dynamically while the machine is operating.
Since sprockets and gears are keyed to their shafts, no dynamic adjustment is normally possible between a sprocket and its own shaft and any correction necessary must be performed by an external mechanism acting between any two shafts that are required to be timed, rather than between a particular sprocket and its own shaft. Power then, is transmitted through such an external mechanism from one machine shaft to another, but in so doing, a change in phase angle is caused to exist between those two machine shafts. Usually this external phase changing mechanism is a controllable differential that can advance or retard the phase relationship. Depending on the design this control can be manual or remote, or both. In most designs the motion passing through is continuous, with internal gears rotating constantly with respect to one another.
Such an external phasing mechanism is wall or floor mounted, having an input and output shaft. Power from the first machinery shaft is transmitted by a chain to the input of the differential and thence by another chain from the differential output to the machinery shaft number two. A multiplicity of shafts require almost a jungle of chains that flow to and from a multiplicity of wall or floor mounted differentials. In addition, each differential requires its own actuating motor or power source to change the phase angle.
For example, many web tension control systems use draw rollers driven by a controllable differential which controls the tension in a web conducted to a web-consuming machine such as a press. The differential is controlled by the output of a tension sensing device such as a movable dancer roller around which the web is trained, with the excursions of the dancer from a fixed reference position being detected by limit switches or the like.
Another application in which the precise timing control of a shaft is essential is the coordination of two or more conveyors. For example, in a given production line it may be necessary to transfer a succession of articles advancing on a horizontal conveyor onto a succession of vertically advancing shelves on a vertical conveyor. Here again, the speeds of the two conveyors may be synchronized by driving one of the conveyors from the main drive by way of a controllable differential. The differential is set to advance or retard the one conveyor relative to the other as needed to assure that the vertical conveyor is in the correct timing position to receive each article leaving the horizontal conveyor.
The maintenance of accurate control over a rotary shaft relative to its driver is especially important in a printing press wherein web is advanced past one or more printing cylinders which print the printed matter in one or more colors. Not only must the motions of the printing cylinders be controlled precisely relative to the advancing web to position the printed matter at the proper location on the web, but also the motions of the cylinders must be synchronized with each other so that the print from each cylinder is in exact registration on the web.
Finally, when controlledly driving shafts or rollers from a main drive shaft, it may be desirable to adjust the phase angle of the roller relative to the main shaft in a forward or reverse direction for purposes of registration or synchronization. During normal operation, it is desirable that the phase change take place quite slowly to avoid overshoot and for optimum accuracy. On the other hand, during initial set-up at the start of a run when the draw rolls are completely out of phase with the drive shaft or in times of emergency, it is desirable that the phase correction take place more quickly to save time and to avoid wastage. All other shaft control apparatus of this general type require external power sources in order to accomplish this and so have the same disadvantages described above.
A more convenient and satisfactory solution to the aforementioned control problems is the provision of a mechanism that mounts on a shaft, acting as an adjustable key, capable of changing the rotational position of a sprocket relative to its own shaft, dynamically and in either direction, drawing the power required for this function from the motion of the sprocket or its shaft without an ancillary power source.
Such a mechanism, then, would be useful in any field requiring machine timing. Such fields, to mention a few, include printing, packaging, collating, machinery timing, boxing, synchronizing, automatic assembly, tension control, and phase shifting.